Cell: The Fundamental Unit of Life - Summary

Robert Hooke (1665): Observed cork cells under a microscope.
- Termed them 'cells' (Latin for 'little room').
- First observation of living things having separate units.
Leeuwenhoek (1674): Discovered free-living cells in pond water using an improved microscope.
Robert Brown (1831): Discovered the nucleus within cells.
Purkinje (1839): Coined 'protoplasm' for the cell's fluid substance.
Schleiden (1838) & Schwann (1839): Proposed cell theory.
- All plants and animals are composed of cells.
- Cell is the basic unit of life.
Virchow (1855): Expanded cell theory.
- All cells arise from pre-existing cells.
1940: Electron microscope enabled observation of complex cell structures.

Cells vary in shape and size based on their specific functions.
Cell Organelles: Specific components within a cell that perform special functions.
- Examples: making new material, waste removal.
- All cells have similar organelles regardless of function or organism.

Plasma Membrane:
- Outermost covering that separates cell contents from the environment.
- Selectively permeable: controls entry/exit of substances.
- Diffusion: Movement of substances (like $CO<em>2$ or $O</em>2$ ) from high to low concentration.
- Osmosis: Diffusion of water across a selectively permeable membrane.
- Hypotonic Solution: Higher water concentration outside the cell; cell gains water and swells.
- Isotonic Solution: Equal water concentration; no net movement.
- Hypertonic Solution: Lower water concentration outside; cell loses water and shrinks.
- Made of lipids and proteins and is flexible.
- Endocytosis: Process of engulfing food and other materials.
Cell Wall (Plant Cells):
- Rigid outer covering outside the plasma membrane, composed of cellulose.
- Provides structural strength.
- Plasmolysis: Shrinkage of cell contents away from the cell wall due to water loss.
Nucleus:
- Contains chromosomes (DNA) for inheritance.
- Controls cell reproduction and chemical activities.
- Prokaryotes: Lack a nuclear membrane; have a nucleoid.
- Eukaryotes: Have a nuclear membrane.
Cytoplasm:
- Fluid content inside the plasma membrane, containing organelles.
- Prokaryotes lack membrane-bound organelles.

Endoplasmic Reticulum (ER):
- Network of membrane-bound tubes and sheets.
- Rough ER (RER): Has ribosomes for protein manufacture.
- Smooth ER (SER): Manufactures lipids; detoxifies poisons and drugs.
- Transports materials within the cell; provides a surface for biochemical activities.
Golgi Apparatus:
- Modifies, packages, and dispatches materials synthesized near the ER.
- Involved in forming lysosomes.
Lysosomes:
- Membrane-bound sacs with digestive enzymes.
- Waste disposal system; digests foreign material and worn-out organelles.
- Known as 'suicide bags' because they can digest their own cell if damaged.
Mitochondria:
- Powerhouses of the cell; release energy in the form of ATP.
- Have their own DNA and ribosomes.
Plastids (Plant Cells Only):
- Chromoplasts: Colored plastids; chloroplasts contain chlorophyll for photosynthesis.
- Leucoplasts: Store materials like starch, oils, and proteins.
- Have their own DNA and ribosomes.
Vacuoles:
- Storage sacs for solid or liquid contents.
- Provide turgidity and rigidity to plant cells.
- Store important substances; help expel excess water and wastes.

Mitosis: Cell division for growth and repair; produces two identical daughter cells.
Meiosis: Cell division for forming gametes; produces four new cells with half the number of chromosomes.